Cardiac electrophysiology refers to the orchestration of electrical pulses that cause the myocardium to contract in a coordinated manner to efficiently pump blood into the arterial tree. Suboptimal physiological alterations that effect the cardiac myocyte milieu can compromise the myocyte function and adversely affect the electrical conduction tissue. As a result, the electrical pulse sequences of the heart may be altered leading to abnormal cardiac sinus rhythms thereby causing dysynchronous or suboptimal myocardial contractile behaviors.
The electrical pulse sequences of the heart may be monitored using an electrocardiography (ECG) device. An ECG device may use multiple electrodes placed across the thorax to obtain millivolt level electrical changes associated with the depolarization of the myocardium and subsequent contraction of the myocardial cells. Typical ECG patterns representing sequences of myocardial repolarization/depolarization events may be referred to as a PQRST ECG tracing.
Contractile abnormalities, as observed in ECG traces, can be characterized as irregular heartbeats or arrhythmias that may manifest as tachycardia, bradycardia, palpitations, or fibrillation. Practitioners having domain expertise in electrocardiology may be able to differentiate abnormal ECG patterns from normal ECG patterns. Practitioners may also be adept at recognizing specific types of arrhythmias via PQRST ECG tracing patterns or behaviors. These ECG patterns provide clues as to the nature or cause of the arrhythmia for purposes enabling treatment that may be part of cardiac health management. For example, arrhythmias can be used to identify numerous forms of physiological dysfunction that include thryroid dysfunction, anemia, myocardial ischemic conditions, and multiple electrical pathways that result in poor cardiac function. In these examples, the recognition of an arrhythmia serves as part of a patient assessment to either diagnose a pathology, thereby enabling its treatment, or top predict onset of a pathology, thereby enabling overall patient management.
Alternatively, cardiac arrhythmias can result from myocardial ischemic conditions and result in decreased cardiac output. Decreased cardiac output may contribute to a hemodynamically unstable physiological state and predispose a patient to life threatening conditions. Therefore, a second purpose of arrhythmia detection may be to serve as part of a real-time hemodynamic monitoring tool. Integral to facilitating this clinical utility can be the ability to characterize the dysrhythmia behavior in terms of the severity of its adverse effect on cardiovascular hemodynamics. Use of physiological feedback of dysfunctional cardiac behavior in concert with other hemodynamic parameters can provide valuable information to characterize the overall physiologic behavior or state of a patient. Measures related to severity of cardiac related hemodynamic instability measures can provide valuable real-time feedback as a part of a hemodynamic monitor to manage patient stability and/or determine appropriate intervention for this purpose.
The pulse waveform obtained from a pulse oximeter, also referred to as a photoplethysmograph, is a mature technology that can be used as a standalone monitor or readily integrated as part of a hemodynamic monitoring system. The photoplethysmograph is not capable of capturing electrophysiology signals. However, patterns based upon temporal alterations of the pulse waveform features can be used to recognize the severity of the adverse hemodynamic impact that the cardiac dysfunction exibits based upon the degree of specific waveform feature abnormality and frequency of incidence. The resultant clinical utility may be to provide either a standalone or component of a hemodynamic monitoring device that enables real-time feedback as a hemodynamic instability monitor based upon pre-identified photoplethysmograph pulse waveform features.